I have a 99 Dodge 2500 Cummins with 130000 miles on it. Within the last few months it has developed a shimmy/vibration at about 35-40 mph and 65-75 mph. It is not a death wobble or anything like that but it is VERY noticeable. I have had the tires balanced 3 times counting when they were installed last year and once at a different tire shop. The guy at the tire shop says it is something rotating: drive shaft/u-joint, tires, etc. I did find the lower u-joint at the diff. with slop between the cup and strap, not the pin and cup which I thought was strange. The experience I have had in the past with u-joints is that it is a sustained consistent vibration through the speed range but I am by no means an expert on the subject. I also have one lower and both upper ball joints with some slop in them. Any ideas???

For starters Replace the bad u-joints or you'll possibly be replacing other parts when the driveshaft flies out. Have you checked suspension components ie tie rods balljoints? Did you have the wheels balanced since you've notice the vibration?

Slop in the ball joints can allow both caster and camber changes, which can cause a shimmy. I'm not so sure a driveshaft u-joint will cause it, but it's not good regardless. Check to see how tight the rod ends are on the steering linkages and the track bar. An easy way to check is to have someone move the wheel back and forth without turning the tires too much. Any 4x4 Dodge owner knows all too well about the slack-on-center in the steering. Obviously, you need to lie on the ground in front of the truck, and it needs to be running, so do this with someone you trust. Make sure the steering damper isn't weak or blown, too.

If the guy at the tire shop is correct. You can diagnois this yourself by supporting the truck by it's rear axle. Thn remove the rear wheels and drums. Run it up to speed and note the vibration.

An out of round tires, bent rim, problem in the sidewall of a tire, tire can still be perfectly balanced.

A bent rim or out of round tire cwill be seen when balancing unless he goes to the guy that works it of his garage using one of those bubble style balancers

1. rotate tires front to back, test drive and see if anything changes, if so change one side and narrow it down to which tire or rim is bad

2. if rotating doesn't change a thing then while driving put in neutral and see if anything changes, if so drivetrain ( if you can take it out of 4 wheel drive do it and see if anything changes )

3. also try touching brakes when shimmy starts and see if anything changes.

you just need to take one step at a time to naeeow it down

good luck!!